Courtney Hartman never gave much though to how gendered kid's clothing can be — that is, until she went shopping for her son and came across pajamas with penguins on them.

A curious thing struck her: There was a pink set and a blue set. The pink outfit featured a penguin with long eyelashes, rosy cheeks and a bow atop its head. The penguin on the blue outfit was chubbier and wore sunglasses and a scarf.

It was a reminder, Hartman told Mic, that "even animals are just really girly or really boyish on clothes."

That was a turning point for Hartman, who went on to found two kid's clothing companies: Jessy & Jack, which offers infant and toddler clothes with gender-neutral designs, and Free to Be Kids, which aims to "flip the script on gender cliches" by selling shirts with empowering messages that break down gendered stereotypes.

A culture that's pushing gender boundaries: Hartman's online companies join other recently founded small businesses with a common goal: to dismantle gender stereotypes in kid's clothing so that children don't feel limited by what they can wear or absorb subliminal messages about how they should behave.

The introduction of these kid's clothing lines comes at a moment when gender boundaries are being increasingly questioned and blurred. On the high-fashion front, designers have gone from merely embracing androgyny to flipping gender expectations entirely (who ever said guys can't wear dresses?).

"From clothing to footwear to technology, forward-thinking companies are enacting a less binary vision of how we shop, dress and live," stated a recent report from market research firm NPD Group. "In fact, millennials are the most tolerant U.S. generation to date: Half of the age group believes gender exists on a spectrum and shouldn't be limited to male and female."

The power of clothing to define kids: Opening clothing up to that fluid, liberated point of view is especially important for kids, whose apparel is often constructed around rigid categories for "girls" and "boys."

Those stereotypes can be constricting for children, and can even limit their development, since boys and girls aren't as likely to play with toys that aren't labeled for specifically for them, research has shown. Target's recent announcement that it will do away with the gender labeling for most store sections, including toys, was an acknowledgment that such labeling can hinder kids' imaginations.

That's why Hartman formally joined nine other like-minded companies this spring to form Clothes Without Limits, a campaign aimed at promoting kids clothing that empowers children to break free from gender stereotypes. They are just a few of the many new companies that have popped up in the past few years with the same goal.

For kids, gendered clothing can influence how they're perceived and are treated, Jo Hadley, the founder of kids' clothing line Handsome in Pink, told Mic.

If a girl is wearing a frilly tutu, she's thought of as being feminine and maybe even dumber or flakier, while boys who like trucks and wear darker colors are deemed masculine, Hadley said. When adults see a girl dressed in "girly" clothing, the conversations focus on their appearance.

"They're not saying to [the little girl], 'Oh, what's going on in school? What books are you reading?'" Hadley said.

Letting kids be who they want to be: Clothing also has the power to subtly direct kids toward what they're supposed to be interested in and how they should act. Colors carry certain connotations, said Hadley, as do prints.

While both of Hadley's children loved pink and purple, it was only socially acceptable for her daughter to wear them, she said.

Meanwhile, her son loved guitars, bikes and fire trucks just as much as he loved pink and purple. Finding shirts with both elements was near impossible, she said. So, in 2007, she started Handsome in Pink with the mindset that "pink can be masculine, blue can be feminine and everyone should feel empowered by what they wear," according to the company website.

Among her bestsellers is a shirt with the message "Forget Princess, Call Me President."

Even within the sphere of "gender-busting clothing" for kids, it's easier to find clothing that's empowering for girls, Hadley said. "If you do not have a boy that loves sports, who just loves trucks ... there's just not a lot of options for them," Hadley said. "It's just not cool to be kind and sensitive and curious."

Part of that stems from persistent gender stigmas about masculinity. Pink, sequins and princess themes remain the purview of girls; if a boy likes any of them, it's taken as a reflection of his masculinity or sexuality, Hadley said.

While girls should certainly be empowered, there's also more work to be done on the boy's front.

"You can't do it in a vacuum," Hartman said. "You can't say that girls have to be able to be tough and smart and like, outgoing, while boys are still within this kind of constrictive box that we put boys in of being only aggressive and never sensitive and sweet."

A bright, stylish future: While not all of the progressive kids companies offer clothing for boys, there is a shared mission for empowering children through what they wear. For Rebecca Melsky, co-founder of Princess Awesome, that means offering designs for girls that are both traditionally feminine and smart — think plenty of pink and colorful dresses with dinosaurs, ninjas and math symbols.

It's a subtle design shift, but one with great impact, which Melsky said she's already seen with her 4-year-old daughter, Eloise.

"When she wears a dress that has pirates on it or that has pi on it, the mathematical symbol, she talks about those things and asks about those things," Melsky said.

Eloise came home one day after preschool last year with a drawing of ice cream cones and what looked like little scribbles. Melksy praised her daughter, who told her to look closer. The tiny scribbles were in fact tiny renderings of pi, Melsky said.